570175f95d
<!-- if this PR closes one or more issues, you can automatically link the PR with them by using one of the [*linking keywords*](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword), e.g. - this PR should close #xxxx - fixes #xxxx you can also mention related issues, PRs or discussions! --> This PR should close #8036, #9028 (in the negative) and #9118. Fix for #9118 is a bit pedantic. As reported, the issue is: ``` > 2023-05-07T04:08:45+12:00 - 2019-05-10T09:59:12+12:00 3yr 12month 2day 18hr 9min 33sec ``` with this PR, you now get: ``` > 2023-05-07T04:08:45+12:00 - 2019-05-10T09:59:12+12:00 208wk 1day 18hr 9min 33sec ``` Which is strictly correct, but could still fairly be called "weird date arithmetic". # Description * [x] Abide by constraint that Value::Duration remains a number of nanoseconds with no additional fields. * [x] `to_string()` only displays weeks .. nanoseconds. Duration doesn't have base date to compute months or years from. * [x] `duration | into record` likewise only has fields for weeks .. nanoseconds. * [x] `string | into duration` now accepts compound form of duration to_string() (e.g '2day 3hr`, not just '2day') * [x] `duration | into string` now works (and produces the same representation as to_string(), which may be compound). # User-Facing Changes ## duration -> string -> duration Now you can "round trip" an arbitrary duration value: convert it to a string that may include multiple time units (a "compound" value), then convert that string back into a duration. This required changes to `string | into duration` and the addition of `duration | into string'. ``` > 2day + 3hr 2day 3hr # the "to_string()" representation (in this case, a compound value) > 2day + 3hr | into string 2day 3hr # string value > 2day + 3hr | into string | into duration 2day 3hr # round-trip duration -> string -> duration ``` Note that `to nuon` and `from nuon` already round-tripped durations, but use a different string representation. ## potentially breaking changes * string rendering of a duration no longer has 'yr' or 'month' phrases. * record from `duration | into record` no longer has 'year' or 'month' fields. The excess duration is all lumped into the `week` field, which is the largest time unit you can convert to without knowing the datetime from which the duration was calculated. Scripts that depended on month or year time units on output will need to be changed. ### Examples ``` > 365day 52wk 1day ## Used to be: ## 1yr > 365day | into record ╭──────┬────╮ │ week │ 52 │ │ day │ 1 │ │ sign │ + │ ╰──────┴────╯ ## used to be: ##╭──────┬───╮ ##│ year │ 1 │ ##│ sign │ + │ ##╰──────┴───╯ > (365day + 4wk + 5day + 6hr + 7min + 8sec + 9ms + 10us + 11ns) 56wk 6day 6hr 7min 8sec 9ms 10µs 11ns ## used to be: ## 1yr 1month 3day 6hr 7min 8sec 9ms 10µs 11ns ## which looks reasonable, but was actually only correct in 75% of the years and 25% of the months in the last 4 years. > (365day + 4wk + 5day + 6hr + 7min + 8sec + 9ms + 10us + 11ns) | into record ╭─────────────┬────╮ │ week │ 56 │ │ day │ 6 │ │ hour │ 6 │ │ minute │ 7 │ │ second │ 8 │ │ millisecond │ 9 │ │ microsecond │ 10 │ │ nanosecond │ 11 │ │ sign │ + │ ╰─────────────┴────╯ ``` Strictly speaking, these changes could break an existing user script. Losing years and months as time units is arguably a regression in behavior. Also, the corrected duration calculation could break an existing script that was calibrated using the old algorithm. # Tests + Formatting ``` > toolkit check pr ``` - 🟢 `toolkit fmt` - 🟢 `toolkit clippy` - 🟢 `toolkit test` - 🟢 `toolkit test stdlib` # After Submitting <!-- If your PR had any user-facing changes, update [the documentation](https://github.com/nushell/nushell.github.io) after the PR is merged, if necessary. This will help us keep the docs up to date. --> --------- Co-authored-by: Bob Hyman <bobhy@localhost.localdomain> |
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nu-parser, the Nushell parser
Nushell's parser is a type-directed parser, meaning that the parser will use type information available during parse time to configure the parser. This allows it to handle a broader range of techniques to handle the arguments of a command.
Nushell's base language is whitespace-separated tokens with the command (Nushell's term for a function) name in the head position:
head1 arg1 arg2 | head2
Lexing
The first job of the parser is to a lexical analysis to find where the tokens start and end in the input. This turns the above into:
<item: "head1">, <item: "arg1">, <item: "arg2">, <pipe>, <item: "head2">
At this point, the parser has little to no understanding of the shape of the command or how to parse its arguments.
Lite parsing
As Nushell is a language of pipelines, pipes form a key role in both separating commands from each other as well as denoting the flow of information between commands. The lite parse phase, as the name suggests, helps to group the lexed tokens into units.
The above tokens are converted the following during the lite parse phase:
Pipeline:
Command #1:
<item: "head1">, <item: "arg1">, <item: "arg2">
Command #2:
<item: "head2">
Parsing
The real magic begins to happen when the parse moves on to the parsing stage. At this point, it traverses the lite parse tree and for each command makes a decision:
- If the command looks like an internal/external command literal: e.g.
fooor/usr/bin/ls, it parses it as an internal or external command - Otherwise, it parses the command as part of a mathematical expression
Types/shapes
Each command has a shape assigned to each of the arguments it reads in. These shapes help define how the parser will handle the parse.
For example, if the command is written as:
where $x > 10
When the parsing happens, the parser will look up the where command and find its Signature. The Signature states what flags are allowed and what positional arguments are allowed (both required and optional). Each argument comes with a Shape that defines how to parse values to get that position.
In the above example, if the Signature of where said that it took three String values, the result would be:
CallInfo:
Name: `where`
Args:
Expression($x), a String
Expression(>), a String
Expression(10), a String
Or, the Signature could state that it takes in three positional arguments: a Variable, an Operator, and a Number, which would give:
CallInfo:
Name: `where`
Args:
Expression($x), a Variable
Expression(>), an Operator
Expression(10), a Number
Note that in this case, each would be checked at compile time to confirm that the expression has the shape requested. For example, "foo" would fail to parse as a Number.
Finally, some Shapes can consume more than one token. In the above, if the where command stated it took in a single required argument, and that the Shape of this argument was a MathExpression, then the parser would treat the remaining tokens as part of the math expression.
CallInfo:
Name: `where`
Args:
MathExpression:
Op: >
LHS: Expression($x)
RHS: Expression(10)
When the command runs, it will now be able to evaluate the whole math expression as a single step rather than doing any additional parsing to understand the relationship between the parameters.
Making space
As some Shapes can consume multiple tokens, it's important that the parser allow for multiple Shapes to coexist as peacefully as possible.
The simplest way it does this is to ensure there is at least one token for each required parameter. If the Signature of the command says that it takes a MathExpression and a Number as two required arguments, then the parser will stop the math parser one token short. This allows the second Shape to consume the final token.
Another way that the parser makes space is to look for Keyword shapes in the Signature. A Keyword is a word that's special to this command. For example in the if command, else is a keyword. When it is found in the arguments, the parser will use it as a signpost for where to make space for each Shape. The tokens leading up to the else will then feed into the parts of the Signature before the else, and the tokens following are consumed by the else and the Shapes that follow.